Isothiourea herbicides

ABSTRACT

Compounds having the formula   &lt;IMAGE&gt;    in which: R is C1-C8 alkyl; or phenyl optionally substituted by 1 or 2 groups selected from C1-C4 alkyl, C1-C4 alkoxy, C1-C4 haloalkoxy, nitro or halo; R1 is C1-C4 alkyl or phenyl; R2 is C1-C4 alkyl; R3 is C2-C4 alkyl or allyl; and X is oxygen, sulfur or NR4 where R4 is hydrogen or C3-C4 alkyl; provided that (i) if R1 is methyl, R is phenyl or substituted phenyl and (ii) if R3 is isopropyl, X is NR4, and R1 is alkyl; and their agriculturally acceptable salts are herbicides.

FIELD OF THE INVENTION

This invention relates to certain isothiourea compounds which demonstrate herbicidal activity.

DESCRIPTION OF THE INVENTION

According to this invention, compounds of the following structure have been found to exhibit herbicidal activity: ##STR2## in which: R is C₁ -C₈ alkyl; or phenyl optionally substituted by 1 or 2 groups selected from C₁ -C₄ alkyl, C₁ -C₄ alkoxy, C₁ -C₄ haloalkoxy, nitro or halo;

R₁ is C₁ -C₄ alkyl or phenyl;

R₂ is C₁ -C₄ alkyl;

R₃ is C₂ -C₄ alkyl or allyl; and

X is oxygen, sulfur or NR₄ where R₄ is hydrogen or C₃ -C₄ alkyl;

provided that

(i) if R₁ is methyl, R is phenyl or substituted phenyl and

(ii) if R₃ is isopropyl, X is NR₄, and R₁ is alkyl; and their agriculturally acceptable salts.

The term "alkyl" includes both straight and branched chain groups having the indicated number of carbon atoms.

Preferred compounds are those in which R is C₂ -C₄ alkyl, phenyl or 4-methoxyphenyl, R₁ is C₃ -C₄ alkyl or phenyl, R₂ is ethyl, R₃ is ethyl or allyl and X is oxygen, sulfur or N-n-propyl.

As used herein, the term "herbicide" means a compound or composition which adversely controls or modifies the growth of plants. By the term "herbicidally effective amount" is meant any amount of such compound or composition which causes an adverse modifying effect upon the growth of plants. By "plants", it is meant germinate seeds, emerging seedlings and established vegetation, including roots and above-ground portions. Such controlling or modifying effects include all deviations from natural development, such as killing, retardation, defoliation, desiccation, regulation, stunting, tillering, leaf burn, dwarfing, and the like.

The compounds of this invention have been found to be active herbicides, as pre- and/or post-emergent herbicides. Pre-emergence herbicides are applied prior to emergence of vegetation from the soil; post-emergence herbicides are applied to control or kill existing vegetation. Some of the compounds of this invention have demonstrated post-emergence herbicidal activity in a relatively short time, and against some weeds, with a very strong effect. Herbicides having such rapid and extensive post-emergence activity are sometimes referred to as "contact-and-burn" or "burn-down" herbicides and are used, among other applications, for clearing vegetation from land such as building lots, highway median strips, railroad track beds, and crop land prior to planting or in minimum till or no-till farming.

Compounds of this invention may be made by the following general process:

(a) reaction of a phosphonic dichloride with an alcohol, thiol or amine: ##STR3##

This reaction is conducted conventionally as known as the art, usually in the presence of a tertiary amine or other suitable base. A small amount of N,N-dimethylaminopyridine may be used as a catalyst. Temperatures generally range from about -40° to about +25° C. at atmospheric pressure. A solvent such as dichloromethane, benzene, ether or the like is used.

(b) reaction with a thioallophanimidate: ##STR4##

This reaction is generally conducted in a solvent, which may be the same solvent used in the preceding step. Temperatures range generally from about 0° to about 25° C at atmospheric pressure. Again, a tertiary amine or other suitable base is employed.

The following are examples of the preparation of compounds of this invention.

EXAMPLE 1 Preparation of ethyl N-(O-(2-butyl)propylphosphonyl)-4-ethylthioallophanimidate

A solution of 2-butanol (0.64 g), triethylamine (0.89 g) and N,N-dimethylaminopyridine (0.05 g) in dichloromethane (8 ml) was added to a solution of propylphosphonic dichloride (1.40 g) in dichloromethane (8 ml) at 0° C. over 10 minutes. After stirring for 5 minutes, the reaction was warmed to room temperature for an additional 5 minutes and then concentrated in vacuo to 2-3 ml. The resulting slurry was cooled to 0° C., and a solution of ethyl 4-ethylthioallophanimidate (1.14 g) and triethylamine (0.89 g) in dichloromethane (8 ml) was added dropwise. After stirring for 5 minutes, the reaction mixture was warmed to room temperature for 20 minutes. The reaction was diluted with dichloromethane (50 ml) and washed successively with 1N hydrochloric acid (30 ml) and saturated sodium bicarbonate (30 ml). The organic layer was dried (Na₂ SO₄), concentrated in vacuo, and the residue was purified by flash chromatography (SiO.sub. 2, 40% ethyl acetate in hexanes) to give ethyl N-(O-(2-butyl)propylphosphonyl)-4-ethylthioallophanimidate. The desired product (0.75 g) was a thick yellow oil.

EXAMPLE 2 Preparation of ethyl N-(O-phenylphenylphosphonyl)-4-ethylthioallophanimidate

A solution of phenol (0.85 g), triethylamine (0.91 g) and N,N-dimethylaminopyridine (0.06 g) in dichloromethane (10 ml) was added to a solution of phenylphosphonic dichloride (1.75 g) in dichloromethane (10 ml) at -40° C. over 15 minutes. Following the addition, the reaction mixture was warmed to 0° C. for 10 minutes. A solution of ethyl 4-ethylthioallophanimidate (1.40 g) and triethylamine (0.91 g) in dichloromethane (5 ml) was then added dropwise. The reaction mixture was allowed to warm to room temperature and stirred for 2 hours. Dichloromethane (25 ml) was added and the reaction mixture was washed with 1N hydrochloric acid (2×25 ml) and saturated sodium bicarbonate (25 ml). The organic layer was dried (Na₂ SO₄), concentrated in vacuo, and the residue purified by flash chromatography (SiO₂, 40% ethyl acetate in hexanes) to give ethyl N-(O-phenylphenylphosphonyl)-4-ethylthioallophanimidate. The desired product (0.40 g ) was a thick yellow oil.

Table I depicts representative compounds of this invention, prepared by a process as described above. Most compounds were obtained as oils. Structures were confirmed by spectroscopic analyses.

                  TABLE I                                                          ______________________________________                                          ##STR5##                                                                      Cpd.                                                                           No.  R          R.sub.1 X       R.sub.2                                                                             R.sub.3                                   ______________________________________                                          1   C.sub.6 H.sub.5                                                                           CH.sub.3                                                                               O       C.sub.2 H.sub.5                                                                     C.sub.2 H.sub.5                            2   C.sub.6 H.sub.5                                                                           i-C.sub.3 H.sub.7                                                                      O       C.sub.2 H.sub.5                                                                     C.sub.2 H.sub.5                            3   C.sub.2 H.sub.5                                                                           i-C.sub.3 H.sub.7                                                                      O       C.sub.2 H.sub.5                                                                     C.sub.2 H.sub.5                            4   C.sub.2 H.sub.5                                                                           C.sub.2 H.sub.5                                                                        O       C.sub.2 H.sub.5                                                                     C.sub.2 H.sub.5                            5   C.sub.2 H.sub.5                                                                           C.sub.6 H.sub.5                                                                        O       C.sub.2 H.sub.5                                                                     C.sub.2 H.sub.5                            6   C.sub.6 H.sub.5                                                                           C.sub.6 H.sub.5                                                                        O       C.sub.2 H.sub.5                                                                     C.sub.2 H.sub.5                            7   C.sub.6 H.sub.5                                                                           n-C.sub.3 H.sub.7                                                                      S       C.sub.2 H.sub.5                                                                     C.sub.2 H.sub.5                            8   C.sub.6 H.sub.5                                                                           s-C.sub.4 H.sub.9                                                                      O       C.sub. 2 H.sub.5                                                                    C.sub.2 H.sub.5                            9   C.sub.6 H.sub.5                                                                           n-C.sub.3 H.sub.7                                                                      N-n-C.sub.3 H.sub.7                                                                    C.sub.2 H.sub.5                                                                     C.sub.2 H.sub.5                           10   C.sub.6 H.sub.5                                                                           s-C.sub.4 H.sub.9                                                                      O       C.sub.2 H.sub.5                                                                     CH.sub.2 CHCH.sub.2                       11   n-C.sub.3 H.sub.7                                                                         s-C.sub.4 H.sub.9                                                                      O       C.sub.2 H.sub.5                                                                     C.sub.2 H.sub.5                           12   n-C.sub.3 H.sub.7                                                                         C.sub.6 H.sub.5                                                                        O       C.sub.2 H.sub.5                                                                     C.sub.2 H.sub.5                           13   n-C.sub.3 H.sub.7                                                                         n-C.sub.3 H.sub.7                                                                      N-n-C.sub.3 H.sub.7                                                                    C.sub.2 H.sub.5                                                                     C.sub.2 H.sub.5                           14   4-CH.sub.3 OC.sub.6 H.sub.4                                                               s-C.sub.4 H.sub.9                                                                      O       C.sub.2 H.sub.5                                                                     C.sub.2 H.sub.5                           15   4-CH.sub.3 OC.sub.6 H.sub.4                                                               i-C.sub.3 H.sub.7                                                                      O       C.sub.2 H.sub.5                                                                     C.sub.2 H.sub.5                           16   n-C.sub.3 H.sub.7                                                                         n-C.sub.3 H.sub.7                                                                      N-n-C.sub.3 H.sub.7                                                                    C.sub.2 H.sub.5                                                                     i-C.sub.3 H.sub.7                         17   n-C.sub.3 H.sub.7                                                                         n-C.sub.3 H.sub.7                                                                      N-n-C.sub.3 H.sub.7                                                                    C.sub.2 H.sub.5                                                                     CH.sub.2 CHCH.sub.2                       18   n-C.sub.3 H.sub.7                                                                         n-C.sub.3 H.sub.7                                                                      N-n-C.sub.3 H.sub. 7                                                                   CH.sub.3                                                                            i-C.sub.3 H.sub.7                         19   n-C.sub.3 H.sub.7                                                                         n-C.sub.3 H.sub.7                                                                      S       C.sub.2 H.sub.5                                                                     C.sub.2 H.sub.5                           ______________________________________                                    

Herbicidal Activity Tests

Compounds 1-19 were tested for herbicidal activity as follows:

The herbicidal effect was observed by comparing the extent of weed control in test flats treated with the compounds against that occurring in similar non-treated control flats. All were applied at 3.57 lb/A (4 kg/ha) to pre-emergence and post-emergence screening flats. An 80 gal/A (748.3 1/ha) spray volume was utilized. Post-emergence flats were seeded 12 days prior to treatment. Pre-emergence flats were seeded one day prior to treatment. Overhead watering of pre-emergence flats and soil surface watering of post-emergence flats, so as to avoid wetting the foliage, were carried out for the duration of the test.

Weed seeds were planted in a flat at a seed depth of 0.5 inch (1.3 cm). Soil for flats was prepared using sandy loam soil fortified with 17-17-17 fertilizer (N-P₂ O₅ -K₂ O on a weight basis) and optionally a fungicide. The test weeds were as follows:

    ______________________________________                                         COMMON NAME        SCIENTIFIC NAME                                             ______________________________________                                         green foxtail      Setaria viridis                                             watergrass         Echinochloa crus-galli                                      wild oat           Avena fatua                                                 annual morning glory                                                                              Ipomoea purpurea                                            velvetleaf         Abutilon theophrasti                                        wild mustard       Sinapsis arvensis                                           yellow nutsedge    Cyperus esculentus                                          ______________________________________                                    

The spray solutions were prepared by dissolving 240 mg of test compound in 20 ml of acetone containing 1% polyoxyethylene sorbitan monolaurate emulsifier, then adding 20 ml of water to the resulting solution. The stock solutions were applied using a linear spray table. Pre-emergence flats are raised to the level of the post-emergence foliage canopy by setting the flats on a wooden block.

The degree of weed control was visually assessed and recorded as percentage control compared to the growth of the same species in an untreated check flat of the same age. The rating scale ranges from 0 to 100%, where 0 equals no effect with plant growth equal to the untreated control, and 100 equals complete kill.

Ratings were taken approximately 15-18 days after treatment (DAT). Results are listed in Table II below, expressed as average control of the three grasses (GR) (wild oat, watergrass, foxtail) and three broadleaf weeds (BL) (morningglory, mustard, velvetleaf), and of nutsedge (NS).

                  TABLE II                                                         ______________________________________                                         (% Control, 4 kg/ha)                                                                  Pre-emergence Post-emergence                                            Compound GR                    GR                                              No.      avg.    BL avg.  NS   avg.  BL avg.                                                                               NS                                 ______________________________________                                         1.       0       0        0    13     83    0                                  2.       0       0        0     7    100    0                                  3.       0       0        0    37     80    0                                  4.       0       0        0    53     90    0                                  5.       0       0        0     0    100    0                                  6.       83      100      0    100   100    10                                 7.       100     100      0    100   100    20                                 8.       100     100      0    100   100    0                                  9.       0       0        0     0     43    0                                  10.      40      100      0    100   100    0                                  11.      100     100      5    86    100    0                                  12.      100     100      5    80    100    0                                  13.      100     100      20   100   100    20                                 14.*     0       3        0     5     76    0                                  15.*     0       0        0     6     23    0                                  16.      0       3        0    28     63    5                                  17.      0       0        0    15      73   0                                  18.      0       5        0    36     51    10                                 19.      81      71       0    35    100    5                                  ______________________________________                                          *tested at 2 kg/ha                                                       

In practice, a pure compound can be used as an herbicide. However, in general, the compounds are first formulated with one or more inert carriers or diluents suitable for herbicidal use, before being applied.

The compositions or formulations, including a compound as described herein, may exist in any one of a number of solid or liquid forms. Examples of liquid forms are emulsifiable concentrates, flowables and pastes. Such compositions may contain, in addition to the active compound or compounds, various carriers or diluents; surface active agents (wetting agents, dispersing agents and/or emulsifying agents); solvents (water, or organic solvents such as aromatic solvents or chlorinated aliphatic solvents); adhesives; thickeners; binders; antifoaming agents; and other substances as mentioned herein. Solid carriers or diluents included in such compositions or formulations may include, for example, ground natural minerals such as kaolins, alumina, calcium carbonate, silica, kieselguhr, clay, etc.; ground synthetic minerals such as various silicates and aluminosilicates and ground vegetable products such as bark, cornmeal, sawdust, cellulose powder and the like.

To manufacture solid compositions, the active substances are mixed with solid carriers or diluents such as those mentioned above and the mixture is ground to the appropriate size. Granules can be manufactured by dissolving an active compound in an organic solvent and applying the mixture, for example, by atomization, onto an absorptive granulated inert material, such as silica. Adhesives may be utilized to assist in the incorporation of the compound onto the solid particles. Pellets or granules can be manufactured by extrusion with appropriate carriers and binders.

Wettable powders, flowables, and pastes are obtained by mixing and grinding an active compound with one or more dispersing agents and/or solid carriers or diluents. Also included may be wetting agents and/or dispersing agents, for example, lignins, methyl cellulose, naphthalenesulfonic acid derivatives, fatty alcohol sulfates and various types of alkali and alkaline earth metal salts of fatty acids.

Emulsifiable concentrates are generally obtained by dissolving the active compound in an organic solvent, for example, butanol, cyclohexanone, xylenes, or higher boiling aromatic hydrocarbons. To obtain suspensions or emulsions in water, wetting agents are generally also added.

The compositions may also be used in the form of microcapsules. Microcapsules consist of fully enclosed or encapsulated droplets or granules containing the active compound, enclosed within an inert porous membrane, so as to permit escape of the encapsulated material into the surrounding medium or environment at a controlled rate.

Useful encapsulating materials include natural and synthetic rubbers or latexes, cellulosic materials, styrene-butadiene copolymers, polyacrylonitriles, polyacrylates, polyesters, polyamides, polyurethanes and starch xanthates.

It is possible to use highly concentrated liquid compositions containing up to about 95% by weight of the active compound, or even the active compound alone for those compounds which are liquids, when applying the compound in the form of a finely divided liquid by use of various atomizing equipment, for example by airplane crop-spraying techniques. For other purposes, however, the various types of compositions which can be utilized for these compounds will contain varying amounts of the compound according to the type of composition and the intended use.

In general, compositions may contain from 0.1 to 95% of the active compound, more preferably from 0.5 to 90%. Some typical compositions will contain an active compound as follows: Wettable powders, flowables and pastes -20 to 90% active compound; oil suspensions, emulsions, solutions and emulsifiable concentrates -5 to 90% active compound; aqueous suspensions -10 to 50% active compound; dusts and powders -1 to 25% active compound; granules and pellets -1 to 20% active compound.

The rate of application of the active compound to a locus to be controlled will depend on the activity of the compound and/or composition and the nature of the seeds and plants to be controlled and will vary from about 0.05 to about 50 pounds per acre (about 0.06 to about 56 kg/ha).

Compositions containing one or more of the active compounds described, in a herbicidally effective amount, may be applied to the plant or locus to be controlled in any conventional manner. Thus, powders and various liquid compositions containing the active compound can be applied by the use of power dusters, boom and hand sprayers and spray spray dusters, or applied from airplanes as mists or sprays. When applied in the latter method, they may be effective in very low dosages. To modify or control growth of germinating seeds or emerging seedlings, liquid compositions may be applied to the soil with conventional methods and may be distributed in the soil to a depth of one-half inch below the soil surface. The compositions need not be admixed with the soil particles, but can be applied merely by sprinkling on the surface of the soil.

Compositions including active compounds may also be applied by addition to irrigation waters supplied to the field to be treated. This method of application permits penetration of the compounds into the soil as the water is absorbed therein.

    ______________________________________                                         EXAMPLES OF TYPICAL COMPOSITIONS                                               ______________________________________                                         Ingredient            Weight %                                                 ______________________________________                                         Oil                                                                            Active Compound        1                                                       Oil solvent-heavy aromatic naphtha                                                                   99                                                       Total                 100                                                      Emulsifiable Concentrate                                                       Active Compound       50                                                       Kerosene              45                                                       Emulsifying agent (mixture of long                                                                    5                                                       chain ethoxylated polyethers with                                              long chain sulfonate)                                                          Total                 100                                                      Active Compound       90                                                       Kerosene               5                                                       Emulsifying agent (mixture of long                                                                    5                                                       chain ethoxylated polyethers with                                              long chain sulfonate)                                                          Total                 100                                                      ______________________________________                                         Dusts and/or Powders                                                           Ingredient        Wt. %    Wt. %    Wt. %                                      ______________________________________                                         Active Compound   0.5      50.0     90.0                                       Attapulgite Clay Powder                                                                          93.5     44.0     4.0                                        Sodium lignin sulfonate                                                                          5.0      5.0      5.0                                        Sodium dioctyl sulfosuccinate                                                                    1.0      1.0      1.0                                        TOTAL             100.0    100.0    100.0                                      ______________________________________                                    

The compositions of the invention may comprise, in addition to one or more compounds of the invention, one or more compounds not of the invention but which possess biological activity. Compounds not of this invention may be other pesticidal agents, such as herbicides, fungicides, insecticides, acaricides, nematocides, bactericides, and plant growth regulators. Such compositions may also contain soil disinfectants or fumigants and may further contain fertilizers, thus making it possible to provide multi-purpose compositions containing one or more of the compounds described herein as well as, optionally, other pesticides and also fertilizers, all intended and formulated for use at the same locus. Accordingly, in yet a still further embodiment, the invention provides an herbicidal composition comprising a mixture of at least one herbicidal compound of formula (I) as hereinbefore defined with at least one other herbicide.

The other herbicide may be any herbicide not having the formula (I). It will generally be an herbicide having a complementary action in the particular application.

Examples of useful complementary herbicides include: regulators. Such compositions may also contain soil disinfectants or fumigants and may further contain fertilizers, thus making it possible to provide multi-purpose compositions containing one or more of the compounds described herein as well as, optionally, other pesticides and also fertilizers, all intended and formulated for use at the same locus. Accordingly, in yet a still further embodiment, the invention provides an herbicidal composition comprising a mixture of at least one herbicidal compound of formula (I) as hereinbefore defined with at least one other herbicide.

The other herbicide may be any herbicide not having the formula (I). It will generally be an herbicide having a complementary action in the particular application.

Examples of useful complementary herbicides include:

A. Benzo-2,1,3-thiodiazin-4-one-2,2-dioxides such as bentazone;

B. hormone herbicides, particularly the phenoxy alkanoic acids such as MCPA, MCPA-thioethyl, dichlorprop, 2,4,5-T, MCPB, 2,4-D, 2,4-DB, mecoprop, trichlopyr, fluroxypyr, clopyralid, and their derivatives (e.g. salts, esters and amides);

C. 1,3-dimethylpyrazole derivatives such as pyrazoxyfen, pyrazolate and benzofenap;

D. Dinitrophenols and their derivatives (e.g. acetates such as DNOC, dinoterb, dinoseb and its ester, dinoseb acetate;

E. dinitroaniline herbicides such as dinitramine, trifluralin, ethalfluralin, pendimethalin; and oryzalin;

F. arylurea herbicides such as diuron, flumeturon, metoxuron, neburon, isoproturon, chlorotoluron, chloroxuron, linuron, monolinuron, chlorobromuron, daimuron, and methabenzthiazuron;

G. phenylcarbamoyloxyphenylcarbamates such as phenmedipham and desmedipham;

H. 2-phenylpyridazin-3-ones such as chloridazon, and norflurazon;

I. uracil herbicides such as lenacil, bromacil and terbacil;

J. triazine herbicides such as atrazine, simazine, aziprotryne, cyanazine, prometryn, dimethametryn, simetryne, and terbutryn;

K. phosphorothioate herbicides such as piperophos, bensulide, and butamifos;

L. thiolcarbamate herbicides such as cycloate, vernolate, molinate, thiobencarb, butylate*, EPTC*, triallate, diallate, ethyl esprocarb, tiocarbazil, pyridate, and dimepiperate;

M. 1,2,4-triazin-5-one herbicides such as metamitron and metribuzin;

N. benzoic acid herbicides such as 2,3,6-TBA, dicamba and chloramben;

O. anilide herbicides such as pretilachlor, butachlor, the corresponding alachlor, the corresponding compound propachlor, propanil, metazachlor, metolachlor, acetochlor, and dimethachlor;

P. dihalobenzonitrile herbicides such as dichlobenil, bromoxynil and ioxynil;

Q. haloalkanoic herbicides such as dalapon, TCA and salts thereof;

R. diphenylether herbicides such as lactofen, fluroglycofen or salts or esters thereof, nitrofen, bifenox, acifluorfen and salts and esters thereof, oxyfluorfen and fomesafen; chlornitrofen and chlomethoxyfen;

S. phenoxyphenoxypropionate herbicides such as diclofop and esters thereof such as the methyl ester, fluazifop and esters thereof, haloxyfop and esters thereof, quizalofop and esters thereof and fenoxaprop and esters thereof such as the ethyl ester;

T. cyclohexanedione herbicides such as alloxydim and salts thereof, sethoxydim, cycloxydim, tralkoxydim, and clethodim;

U. sulfonyl urea herbicides such as chlorosulfuron, sulfometuron, metsulfuron and esters thereof; benzsulfuron and esters thereof such as the ester thereof methyl, DPX-M6313, chlorimuron and esters such as the ethyl ester thereof, pirimisulfuron and esters such as the methyl ester thereof, DPX-LS300 and pyrazosulfuron;

V. imidazolidinone herbicides such as imazaquin, imazamethabenz, imazapyr and isopropylammonium salts thereof, imazethapyr;

W. arylanilide herbicides such as flamprop and esters thereof, benzoylprop-ethyl, diflufenican;

X. amino acid herbicides such as glyphosate and gluyfosinate and their salts and esters, sulphosate, and bilanafos;

Y. organoarsenical herbicides such as MSMA;

Z. herbicidal amide derivative such as napropamide, propyzamide, carbetamide, tebutam, bromobutide, isoxaben, naproanilide, diphenamid, and naptalam;

AA. miscellaneous herbicides including ethofumesate, cinmethylin, difenzoquat and salts thereof such as the methyl sulfate salt, clomazone, oxadiazon, bromofenoxim, barban, tridiphane, (in the ratio 3:1) flurochloridone, quinchlorac and mefanacet;

BB. examples of useful contact herbicides include bipyridylium herbicides such as those in which the active entity is paraquat and those in which the active entity is diquat. 

What is claimed is:
 1. A compound having the formula ##STR6## in which: R is C₁ -C₈ alkyl; or phenyl optionally substituted by 1 or 2 groups selected from C₁ -C₄ alkyl, C₁ --C₄ alkoxy, C₁ -C₄ haloalkoxy, nitro or halo;R₁ is C₁ -C₄ alkyl or phenyl; R₂ is C₁ -C₄ alkyl; R₃ is C₂ -C₄ alkyl or allyl; and X is oxygen, sulfur or NR₄ where R₄ is hydrogen or C₃ -C₄ alkyl;provided that (i) if R₁ is methyl, R is phenyl or substituted phenyl and (ii) if R₃ is isopropyl, X is NR₄, and R₁ is alkyl; and agriculturally acceptable salts thereof.
 2. A compound according to claim 1 in which R is C₂ -C₄ alkyl, phenyl is 4-methoxyphenyl; R₁ is C₃ -C₄ alkyl or phenyl; R₂ is ethyl; and R₃ is ethyl or allyl.
 3. A compound according to claim 1 in which R is n-propyl or phenyl; R₁ is phenyl, n-propyl or sec-butyl; R₂ is ethyl; R₃ is ethyl or allyl; X is oxygen, sulfur or NR₄ and R₄ is n-propyl.
 4. A compound according to claim 3 in which R is phenyl, X is oxygen and R₁ is sec-butyl.
 5. A compound according to claim 3 in which R is n-propyl and R₃ is ethyl.
 6. A compound according to claim 3 in which R is n-propyl, R₁ is n-propyl, X is NR₄ and R₄ is n-propyl.
 7. A method of controlling undesirable vegetation comprising applying to said vegetation or the locus thereof, a herbicidally effective amount of a compound according to claim
 1. 8. A method according to claim 7 in which the compound is applied subsequent to the emergence of the vegetation at the locus.
 9. A herbicidal composition comprising:a) a herbicidally effective amount of a compound according to claim 1; and b) a diluent or carrier suitable for use with herbicides. herbicides. 